Next.js 16.4 makes Cache Components the default caching path

Next.js 16.4 ships with Cache Components as the recommended approach, enabled by default for new create-next-app projects, plus a next upgrade --agent mode that lets a coding agent drive the upgrade. Existing apps do not adopt the new caching model automatically — that remains a separate migration.

• Cache Components are on by default only for new create-next-app projects
• next upgrade --agent automates the mechanical parts of the upgrade
• One benchmark: a 1,555-page build dropped from 83.9s to 49.1s
• Caching is now declared per component and function via use cache